Date of Award

Spring 2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical & Computer Engineering

Program/Concentration

Computer Engineering

Committee Director

Min Song

Committee Member

Frederic D. McKenzie

Committee Member

Hussein M. Abdel-Wahab

Call Number for Print

Special Collections LD4331.E55 R59 2005

Abstract

Multiuser detection is a technique to improve the capacity and coverage in a code division multiple access (CDMA) system. Being a critical component of this technique, the maximum likelihood (ML) multiuser receiver has received extensive study. Multiuser detection is an important technology in wireless CDMA systems for improving both data rate as well as the user capacity. However, the computational complexity of this receiver prevents from the widespread use of this technique. Due to the high computational complexity, most of the CDMA systems today and in the near future will continue to use the conventional match filter with comparatively low user capacity and a slow data rate.

While many multiuser detectors could achieve optimal performance, they suffer from their relatively higher complexity that prevents CDMA systems to adapt this technology for signal detection. However, if we could lower the computational complexity of multiuser detectors, most of the CDMA systems would likely to get advantage of this technique in terms of increased system capacity and a better data rate. In this thesis, a novel approach for reducing the asymptotic computational complexity of multiuser receivers is proposed that utilizes the transformation matrix technique to improve the performance of multiuser detectors. By using the proposed algorithm, the computational complexity of multiuser detectors can be reduced by several orders of magnitude. This is done by realizing that much of the processing performed is unnecessary. Since most of the decisions are correct, we can reduce the number of computations by using the transformation matrixes only on those coordinates that are most likely lead to an incorrect decision. By doing this, we can greatly reduce the unnecessary processing that requires making a decision about the correct region or the coordinate. Thus, this reduction in the computational complexity would likely to give us a considerable improvement in the performance of multiuser receivers. The performance measure adopted in this thesis is the achievable bit rate for a fixed probability of error (10"7) and the consistent values of SNR.

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DOI

10.25777/9xmq-5384

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